In telecommunications systems that have a point-to-point topology (e.g., leased telephone lines, microwave radio), the entire bandwidth of the communications channel is available to a single terminal without its having to contend for access to the channel with other terminals. In contrast, in telecommunications systems that have a point-to-multipoint topology (e.g., broadcast radio, shared channel wireline networks) the common communications channel is shared by multiple terminals, each of which must contend with other terminals for access to the bandwidth of the channel.
Given the characteristics of shared transmission medium networks, a number of techniques, called "multi access layer protocols," have been developed to resolve the contention issue and to ensure the efficient utilization of the bandwidth of the common communications channel.